Conventionally, for a lithium secondary battery, LiCoO2 is mainly used as a positive active material. However, a lithium secondary battery using LiCoO2 as a positive active material has a discharge capacity of about 120 to 130 mAh/g and is also inferior in thermal stability in the battery inside in a charging state.
Therefore, materials obtained by forming solid solutions of LiCoO2 with other compounds are known as the active material for a lithium secondary battery. That is, as an active material for a lithium secondary battery, Li[Co1−2xNixMnx]O2 (0<x≦½), which is a solid solution having an α-NaFeO2 type crystal structure shown on a ternary phase diagram of three components, LiCoO2, LiNiO2, and LiMnO2, was disclosed in 2001. A lithium secondary battery using one example of the above-mentioned solid solutions, LiNi1/2Mn1/2O2 or LiCo1/3Ni1/3Mn1/3O2 has a discharge capacity of 150 to 180 mAh/g and is thus more excellent than that using LiCoO2 and also more excellent in thermal stability in the battery inside in a charging state than that using LiCoO2.
However, an active material for a lithium secondary battery with a further higher discharge capacity has been required.
Patent Documents 1 to 4 disclose compounds obtained by adding Fe to Li[Li1/3Mn2/3]O2 as active materials for a lithium secondary battery. Patent Documents 5 to 8 disclose compounds obtained by adding Fe and Ni to Li[Li1/3Mn2/3]O2 as active materials for a lithium secondary battery.
However, although being characterized in that economical iron is used as a raw material, lithium secondary batteries using the materials of the inventions disclosed in Patent Documents 1 to 8 have high polarization as compared with those using conventional positive active materials and are not also excellent in discharge capacity.
Patent Documents 9 and 10 disclose LiNiO2—Li[Li1/3Mn2/3]O2 type solid solutions as active materials for a lithium secondary battery.
However, the active materials for a lithium secondary battery disclosed in Patent Documents 9 and 10 have a problem that their synthesis needs to be carried out in oxygen and synthesis in air is difficult since the electron state of Ni is Ni3+. As described above, also in terms of the industrial handling easiness, an active material for a lithium secondary battery in which Ni is present in form of Ni2+ is desired. Further, since merely one electron reaction of Ni3+→Ni4+ is employed in this material, improvement of the discharge capacity of a lithium secondary battery cannot be expected.
Patent Documents 11 and 12 disclose LiNi1/2Mn1/2O2—Li[Li1/3Mn2/3]O2 type solid solutions and the like as active materials for a lithium secondary battery.
However, the discharge capacities of lithium secondary batteries using the materials disclosed in Patent Documents 11 and 12 are far from improvement; the discharge capacities are inferior to those in the case of using LiNi1/2Mn1/2O2 alone.
Patent Documents 13 and 14 disclose materials obtained by allowing Li[Li1/3Mn2/3]O2 to be present on the particle surfaces of LiMeO2 (Me: Co, Ni) as active materials for a lithium secondary battery.
However, the techniques disclosed in Patent Documents 1 to 14 and the techniques disclosed in Patent Documents 15 to 18 described below all fail to improve the discharge capacity, which is an object of the present invention.
Disclosing a concept of employing solid solutions of three components, Li[Ni1/2Mn1/2]O2, Li[Li1/3Mn2/3]O2, and LiCoO2 as a basic structure, Patent Documents 15 and 16 contain descriptions as follows:
“The present invention provides a layered lithium transition metal composite oxide supposed to form a solid solution of
                Li[Ni1/2Mn1/2]O2 at a ratio of (1−3x)(1−y)        Li[Li1/3Mn2/3]O2 at a ratio of 3x(1−y), and        LiCoO2 at a ratio of y,and having a layered structure, that is, a basic structure of [Li](3a)[(LixNi(1−3x)/2Mn(1+x)/2)(1−y)Coy](3b)O2 . . . (II), wherein (3a) and (3b) respectively represent different metal sites in the layered R(−3)m structure”, “However, the important point of the present invention is that z mol of Li is added excessively to the composition represented by the formula (II) and a solid solution represented as[Li](3a)[Liz/(2+z){(LixNi(1−3x)/2Mn(1+x)/2)(1−yCoy}2/(2+z)](3b)O2  (I)(wherein, 0.01≦x≦0.15; 0≦y≦0.35; 0.02(1−y)(1−3x)≦z≦0.15(1−y)(1−3x)); and (3a) and (3b) respectively represent different metal sites in the layered R(−3)m structure.” However, also with reference to Comparative Examples, merely those having excess amounts of Li beyond the amounts obtained spontaneously in the case of assuming such solid solutions are concretely described and there is no description that the discharge capacity can be improved by specifying the ratios of those three components in the composition range in which the Li amount is made not to be intentionally in excess.        
Patent Document 17 discloses the composition formula: (Li[Ni(x−y)Li(1/3−2x/3)Mn(2/3−x/3−y)Co2y]O2 (0<x≦0.5; 0≦y≦⅙; x>y) in claim 1.
The composition formula disclosed in claim 1 of Patent Document 17 partially overlaps the composition range of the present invention as a broader concept; however there is no description implying the technical idea of employing the solid solution of three components of Li[Ni1/2Mn1/2]O2, Li[Li1/3Mn2/3]O2, and LiCoO2 and the range showing the above-mentioned composition formula widely includes compositions other than those of the solid solution of three components of Li[Ni1/2Mn1/2]O2, Li[Li1/3Mn2/3]O2, and LiCoO2.
Patent Document 18 discloses the composition formula: (Li[Ni(x−y) Li(1/3−2x/3)Mn(2/3−x/3−y)Co2y]O2 (wherein x is more than 0 and 0.5 or less; y is 0 or more and ⅙ or less, and x>y) in claim 2.
The composition formula disclosed in claim 2 of Patent Document 18 partially overlaps the composition range of the present invention as a broader concept; however as Examples, merely “a compound represented by the composition formula Li[Ni0.5Mn0.5]O2” and “a compound represented by the composition formula Li[Ni0.4Mn0.4Co0.2]O2” are concretely disclosed and they are completely out of the composition range of the present invention. Further, there is no description implying the technical idea of employing the solid solution of three components of Li[Ni1/2Mn1/2]O2, Li[Li1/3Mn2/3]O2, and LiCoO2.
Patent Document 19 discloses a method for synthesizing Li[Co1−2xNixMnx]O2 having an α-NaFeO2 type crystal structure by producing a hydroxide of transition metals (Co, Ni, Mn) by a coprecipitation method, mixing the hydroxide with a lithium compound, and calcining the mixture.
Patent Document 1: JP-A No. 2002-068748
Patent Document 2: JP-A No. 2002-121026
Patent Document 3: Japanese Patent No. 03500424
Patent Document 4: JP-A No. 2005-089279
Patent Document 5: JP-A No. 2006-036620
Patent Document 6: JP-A No. 2003-048718
Patent Document 7: JP-A No. 2006-036621
Patent Document 8: Japanese Patent No. 03940788
Patent Document 9: JP-A No. 09-055211
Patent Document 10: Japanese Patent No. 03539518
Patent Document 11: JP-A No. 2004-158443
Patent Document 12: Japanese Patent No. 03946687
Patent Document 13: JP-A No. H08-17935
Patent Document 14: Japanese Patent No. 03258841
Patent Document 15: JP-A No. 2006-253119
Patent Document 16: JP-A No. 2007-220475
Patent Document 17: JP-A No. 2004-006267
Patent Document 18: JP-A No. 2004-152753
Patent Document 19: International Publication No. 02/086993
Non-patent Document 1 discloses preparation and electrochemical properties of a solid solution of LiCoO2—LiNi0.5Mn0.5O2—Li2MnO3 with a high Mn amount and concretely discloses    0.36LiCoO2-0.2LiNi1/2Mn1/2O2-.0.44Li2MnO3,    0.27LiCoO2-0.2LiNi1/2Mn1/2O2-0.53Li2MnO3,    0.18LiCoO2-0.2LiNi1/2Mn1/2O2-0.62Li2MnO3, and    0.09LiCoO2-0.2LiNi1/2Mn1/2O2-0.71Li2MnO3; however in a case where the Li content is as high as 1.4 to 1.5, the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1.4 (see FIG. 2), which is not 1.56 or higher, and therefore, these solid solutions are apparently different from the active material of the present invention. Further, with respect to the production method, only calcining at 750 to 950° C. after decomposition of respective acetic acid salts at 400° C. by a spray drying method is described but no method of employing a coprecipitation method is described. Moreover, although the discharge capacity is increased to be 200 mAh/g or higher in a potential region of 3.0 to 4.6 V, an increase of the discharge capacity in a potential region of 4.3 V or lower is not indicated.
Non-patent Document 2 discloses that with respect to Li[Li0.182Ni0.182Co0.091Mn0.545]O3, that is, a layered material of 0.545Li[Li1/3Mn2/3]O2-0.364LiNi1/2Mn1/2O2-0.091LiCoO2, the discharge capacity is 200 mAh/g or higher in a potential region of 4.6 V to 2.0 V of an initial period and about 160 mAh/g in a potential region of 4.3 V to 2.0 V after cycles in 4.6 V to 2.0 V and therefore, this layered material does not have a high discharge capacity in the potential region of 4.3 V or lower. Further, the layered material is produced by producing a slurry of respective acetic acid salts, drying the slurry at 120° C. and calcining the dried product at 900° C. and thus is not produced by a coprecipitation method and the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1, which is not 1.56 or higher, and therefore, the material is apparently different from the active material of the present invention.
Non-patent Document 3 discloses that as a positive active material of a lithium battery, 0.7Li2MnO3.0.3LiMn0.33Ni0.33Co0.33O2 and 0.5Li2MnO3.0.5LiMn0.33Ni0.33Co0.33O2 are shown and with respect to the former, the discharge capacity is 261 mAh/g at 4.8 V charge at 50° C. and 200 mAh/g at 4.6 V charge at 50° C., but improvement of the discharge capacity in a potential region of 4.3 V or lower is not described. Further, the above-mentioned positive active materials are produced by mixing a coprecipitated hydroxide of Co, Ni, and Mn with LiOH, pre-sintering the mixture at 300 or 500° C., and calcining the pre-sintered product at 800 to 1000° C. and the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1, which is not 1.56 or higher, and therefore, the materials are apparently different from the active material of the present invention.
Non-patent Document 4 discloses Li[Li1/5Ni1/10Co1/5Mn1/2]O2, that is, a solid solution having a layered crystal structure of 0.6Li[Li1/3Mn2/3]O2-0.2LiNi1/2Mn1/2O2-0.2LiCoO2, and the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1.4 (see FIG. 3), which is not 1.56 or higher, and therefore, the solid solution is apparently different from the active material of the present invention. Further, with respect to the production method, merely a sol-gel method using respective acetic acid salts is described, and production by using a coprecipitation method is not described. Moreover, although the discharge capacity is described to be 229 mAh/g at 4.5 V; improvement of the discharge capacity in a potential region of 4.3 V or lower is not described.
Non-patent Document 5 discloses an active material of (1−2x)LiNi1/2Mn1/2O2.xLi[Li1/3Mn2/3]O2.xLiCoO2 (0≦x≦0.5), and 0.2LiNi1/2Mn1/2O2.0.4Li[Li1/3Mn2/3]O2.0.4LiCoO2, 0.5Li[Li1/3Mn2/3]O2-0.5LiCoO2 or the like satisfying the composition formula has composition close to that of the present invention but not in the range of the composition of the present invention. Further, with respect to the production method, merely a solid-phase method using respective acetic acid salts is described, and production using a coprecipitation method is not described. Moreover, since the discharge capacity is about 190 mAh/g at 4.6 V (x=0.4), the discharge capacity in a potential region of 4.3 V or lower is not so high.
Non-patent Document 6 discloses a positive active material of LiNi0.20Li0.20Mn0.60O2, that is, 0.6Li[Li1/3Mn2/3]O2-0.4LiNi1/2Mn1/2O2, and the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1.7 (see FIG. 7) and the intensity of the diffraction peak of the (104) plane becomes higher than the intensity of the diffraction peak of the (003) plane after discharge, and therefore, this positive active material is apparently different from the active material of the present invention. Further, with respect to the production method, merely a method of calcining powders obtained by heat decomposition of respective acetic acid salts or nitric acid salts is described, and production by using a coprecipitation method is not described. Moreover, the discharge capacity is described to be 288 mAh/g at 4.8 V charge in the initial period and 220 mAh/g after 20 cycles; however improvement of the discharge capacity in a potential region of 4.3 V or lower is not described.
Non-patent Document 7 discloses a positive active material of a layered structure of (1−x−y)LiNi1/2Mn1/2O2.xLi[Li1/3Mn2/3]O2.yLiCoO2 (0≦x=y≦0.3 and x+y=0.5) and since the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry of 0.5LiNi1/2Mn1/2O2.0.5Li[Li1/3Mn2/3]O2 satisfying the composition formula is about 1.4, which is not 1.56 or higher, and therefore, the positive active material is apparently different from the active material of the present invention. Further, with respect to the production method, merely a solid-phase method using respective acetic acid salts is described, and production using a coprecipitation method is not described. Moreover, since the discharge capacity is about 180 mAh/g at 4.6 V, the discharge capacity in a potential region of 4.3 V or lower is not so high.
Non-patent Document 8 discloses a solid solution with a layered structure of 0.5Li(Ni0.5Mn0.5)O2-0.5Li(Li1/3Mn2/3)O2, and in Q24, which is a solid solution of a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1.2, which is not 1.56 or higher, and therefore, this solid solution is apparently different from the active material of the present invention. In S24 and VS24, the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is 1.56 or higher; however many peaks of impurities are observed and they are not specified as the solid solution of a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure. Further, with respect to the production method, merely a method of calcining precursors from respective acetic acid salts is described, and production using a coprecipitation method is not described. Moreover, although the discharge capacity of Q24 is about 210 mAh/g at 4.6 V charge, improvement of the discharge capacity in a potential region of 4.3 V or lower is not described. S24 and VS24 are those having small discharge capacities.
Non-patent Document 9 discloses electrochemical properties of a solid solution of Li(Li(1−x)/3CoxMn(2−2x)/3O2) (0≦x≦1), and in Li(Li0.7/3Co0.3Mn1.4/3O2) satisfying the composition formula, that is, 0.7Li[Li1/3Mn2/3]O2-0.3LiCoO2, and Li(Li0.6/3Co0.4Mn1.2/3O2), that is, 0.6Li[Li1/3Mn2/3]O2-0.4LiCoO2, the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1.3, which is not 1.56 or higher, and therefore, this solid solution is apparently different from the active material of the present invention. Further, with respect to the production method, merely a method of calcining precursors from respective acetic acid salts is described, and production using a coprecipitation method is not described. Moreover, although the discharge capacity is described to be about 250 mAh/g at 4.6 V charge, improvement of the discharge capacity in a potential region of 4.3 V or lower is not described.
Non-patent Document 10 discloses synthesis, structure, and electrochemical behaviors of Li[NixLi1/3−2x/3Mn2/3−x/3]O2 and with respect to the production method, production using a coprecipitation method is described; however in Li[Ni0.25Li1/6Mn7/12]O2 satisfying the composition formula, that is, a solid solution of 0.5Li[Li1/3Mn2/3]O2-0.5LiNi1/2Mn1/2O2 and the like, the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1, which is not 1.56 or higher, and therefore, the solid solution is apparently different from the active material of the present invention. Further, although the discharge capacity is described to be about 220 mAh/g at 4.8 V charge, improvement of the discharge capacity in a potential region of 4.3 V or lower is not described (based on the observation of the charge-discharge curve, about 150 mAh/g in terms of 4.3 V).
Non-patent Document 11 discloses synthesis and electrochemical properties of a compound of Li[CoxLi(1/3−x/3)Mn(2/3−2x/3)]O2, and in a compound of Li[Co0.33Li0.67/3Mn1.34/3]O2 satisfying the composition formula, that is, a compound of 0.67Li[Li1/3Mn2/3]O2-0.33LiCoO2, the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1.4, which is not 1.56 or higher, and therefore, this compound is apparently different from the active material of the present invention. Further, with respect to the production method, merely a method of calcining powders obtained by heat decomposition of respective acetic acid salts or nitric acid salts is described, and production by using a coprecipitation method is not described. Moreover, although the discharge capacity is described to be about 200 mAh/g at 4.6 V charge, improvement of the discharge capacity in a potential region of 4.3 V or lower is not described (based on the observation of the charge-discharge curve, about 150 to 160 mAh/g in terms of 4.3 V).
Non-patent Document 12 discloses the results of X-ray diffractometry of a positive active material of Li(Li0.2Ni0.2Mn0.6)O2 for a lithium secondary battery, that is, a positive active material of 0.6Li[Li1/3Mn2/3]O2-0.4LiNi1/2Mn1/2O2 and that the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane is about 1.6 and 1.7 after discharge is described; however it is about 1.2, which is not 1.56 or higher, after synthesis and before discharge and therefore, the positive active material is apparently different from the active material of the present invention. Further, with respect to the production method, merely a sol-gel method using respective acetic acid salts is described, and production using a coprecipitation method is not described. Moreover, although the discharge capacity is about 200 mAh/g in a potential region of 2.0 to 4.6 V, the discharge capacity is about 110 mAh/g in a potential region of 2.0 to 4.3 V after 4.6 V charge and therefore, the discharge capacity in the potential region of 4.3 V or lower is not so high.
Non-patent Document 13 discloses a nanocrystal of Li[Li0.2Ni0.2Mn0.6]O2, that is 0.6Li[Li1/3Mn2/3]O2-0.4 LiNi1/2Mn1/2O2, and the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1.3, which is not 1.56 or higher, and therefore, this nanocrystal is apparently different from the active material of the present invention. Further, with respect to the production method, merely a method of calcining powders obtained by heat decomposition of respective acetic acid salts or nitric acid salts is described, and production by using a coprecipitation method is not described. Moreover, although the discharge capacity is described to be about 210 mAh/g at 4.8 V charge, improvement of the discharge capacity in a potential region of 4.3 V or lower is not described.
Non-patent Document 14 discloses preparation and electrochemical behaviors of a solid solution of LiCoO2—Li2MnO3(Li[Li(x/3)Co(1−x)Mn(2x/3)]O2), and in Li[Li0.2Co0.4Mn0.4]O2 satisfying the composition formula, that is, a solid solution of 0.6Li[Li1/3Mn2/3]O2-0.4LiCoO2 and Li[Li0.23Co0.31Mn0.46]O2, that is, a solid solution of 0.69Li[Li1/3Mn2/3]O2-0.31LiCoO2, the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry (see FIG. 2) is about 2.3 and 1.9, respectively, before charge-discharge, which is 1.56 or higher; however at the end of charge with a charge capacity of 160 mAh or higher, the intensity ratio is considerably lowered (1.4 to 1.7 for the former solid solution, see FIG. 10) and the intensity ratio at the end of discharge in the case of discharge of the active material (solid solution) with the considerably lowered intensity ratio is not made clear and therefore, the active materials cannot be said to be the same as the active material of the present invention. Further, with respect to the production method, merely a method of decomposing respective acetic acid salts at 400° C. by a spray drying method and thereafter, calcining at 750 to 950° C. is described, and production using a coprecipitation method is not described. Moreover, the discharge capacity is about 100 mAh/g at 4.5 V charge and thus it is not so high.
Non-patent Document 15 discloses a positive active material of a layered structure of 0.6LiNi0.5Mn0.5O2.xLi2MnO3.yLiCoO2 (x+y=0.4), and in 0.6LiNi0.5Mn0.5O2.0.4Li2MnO3 satisfying the composition formula, the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1.4, which is not 1.56 or higher, and therefore, this positive active material is apparently different from the active material of the present invention. Further, with respect to the production method, merely a method of calcining powders obtained by heat decomposition of respective acetic acid salts is described, and production using a coprecipitation method is not described. Moreover, although the discharge capacity is described to be about 210 mAh/g at 4.6 V charge, improvement of the discharge capacity in a potential region of 4.3 V or lower is not described (about 150 mAh/g in terms of 4.3V).
Non-patent Document 16 discloses a positive active material of Li[Li0.15Ni0.275Mn0.575]O2 for a lithium secondary battery, that is, a positive active material of 0.45Li[Li1/3Mn2/3]O2-0.55LiNi1/2Mn1/2O2 and the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1, which is not 1.56 or higher, and therefore, this positive active material is apparently different from the active material of the present invention. Further, with respect to the production method, merely a sol-gel method using respective acetic acid salts is described, and production using a coprecipitation method is not described. Moreover, although the discharge capacity is described to be about 180 mAh/g at 4.6 V charge, improvement of the discharge capacity in a potential region of 4.3 V or lower is not described (about 140 mAh/g in terms of 4.3V).
Non-patent Document 17 discloses synthesis and electrochemical properties of Li[Li(1−2x)/3NixMn(2−x)/3]O2 as a positive active material for a lithium secondary battery, and in Li[Li0.15Ni0.275Mn0.575]O2 satisfying the composition formula, that is, a positive active material of 0.45Li[Li1/3Mn2/3]O2-0.55LiNi1/2Mn1/2O2, the intensity ratio I(003)/I(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry is about 1, which is not 1.56 or higher, and therefore, the positive active material is apparently different from the active material of the present invention. Further, with respect to the production method, merely a sol-gel method using respective acetic acid salts is described, and production using a coprecipitation method is not described. Moreover, although the discharge capacity is described to be about 190 mAh/g at 4.6 V charge, improvement of the discharge capacity in a potential region of 4.3 V or lower is not described (about 140 mAh/g in terms of 4.3V).
Non-patent Document 1: Electrochimica Acta 51 (2006)5581-5586
Non-patent Document 2: Electrochemistry Communications 7 (2005)1318-1322
Non-patent Document 3: Electrochemistry Communications 9 (2007)787-795
Non-patent Document 4: Journal of Power Sources 146 (2005)281-286
Non-patent Document 5: Journal of Power Sources 146 (2005)598-601
Non-patent Document 6: Solid State Ionics 176 (2005)1035-1042
Non-patent Document 7: Journal of The Electrochemical Society, 152(1)A171-A178 (2005)
Non-patent Document 8: Journal of Power Sources 124 (2003)533-537
Non-patent Document 9: Electrochemistry Communications 9 (2007)103-108
Non-patent Document 10: Journal of The Electrochemical Society, 149(6)A777-A791 (2002)
Non-patent Document 11: Journal of The Electrochemical Society, 151(5)A720-A727 (2004)
Non-patent Document 12: Electrochemical and Solid-State Letters, 6(9) A183-A186 (2003)
Non-patent Document 13: Electrochemical and Solid-State Letters, 6(8) A166-A169 (2003)
Non-patent Document 14: Journal of Power Sources 159 (2006)1353-1359
Non-patent Document 15: Materials Letters 58 (2004)3197-3200
Non-patent Document 16: Journal of Materials Chemistry, 2003, 13, 319-322
Non-patent Document 17: Journal of Power Sources 112 (2002)634-638